This invention relates to a method of consolidating a gravel pack by use of controlled melting point materials and heat.
In many oil or gas bearing formations, as well as water sands, the particles comprising the formation are not effectively cemented together, which results in the formation either being substantially unconsolidated or only loosely consolidated. These formations are oridinarily comprised of sands or sandstone. When fluids are produced from such formations, solid particles from the formation flow into the wellbore. If these formation fluids in the unconsolidated formations are under high pressure, the solid particles will flow through the tubing and other equipment in the wellbore at high velocities, causing severe erosion of well equipment. If the flow rates are not at high velocities, the solid particles flow into the wellbore and plug the tubing. It is then necessary to perform expensive work-over operations on the well to place it back in operation. In extreme cases, the unconsolidated oil-bearing formation surrounding the well is washed out, and undermines the overlying formations penetrated by the wellbore with the result that those formations sometimes collapse and damage the well.
Several methods have been used to combat the flow of sands into the wellbore from unconsolidated formations. One such method is to set a slotted liner in the borehole through the producing formation and produce formation fluids through the slots of the liner. Sometimes the setting of the slotted liner is combined with a gravel packing operation in which gravel is packed around the liner to provide support for the unconsolidated formation. Both of these methods have the shortcoming that sands in the incompetent formation are still free to move and therefore can plug the gravel pack or liner. Because the gravel pack is comprised of gravel that is not adhered together, the gravel is free to move to allow formation sand to work its way through the gravel pack to plug the liner. This is especially true when the formation pressure has diminished such that the well is placed on the pump. The pulsating suction caused by the up and down movement of the pump keeps the gravel in a turbulent state such that it is easy for a formation sand to penetrate through it. To prevent this, it has been suggested that particles in the gravel pack be treated by a resin which coats the gravel pack particles, followed by condensation or polymerization to bond the particles into a unitary mass. Care must be taken to insure preservation of the permeability of the gravel pack after the resin treatment. Special resins are often used which have a high shrinkage factor upon drying such that the shrinkage provides permeability of the gravel pack. Control of the condensation or polymerization of the resin is extremely difficult because of the remoteness of the operation.
Another method that has been suggested to stabilize unconsolidated formations is to displace into the formation a mixture of liquid plastic in a catalyst for setting the plastic. In theory, the mixture will coat the sand particles and the plastic will act as a bonding agent when set by the catalyst. The main problems with this procedure are the maintenance of a proper mixture of catalyst and plastic, and in addition, a critical time factor arises. These two problems are interrelated in that an improper mixture can cause an extremely long or an extremely short set up time. In addition, plastics not contacted by the catalysts will be unlikely to ever set up. Thus, the plastic will flow into the wellbore when the well is returned to production. When the liquid catalyst has been premixed with the plastic, there is a limited amount of time in which the mixture can be placed in the formation. If a delay occurs in placement of the mixture, the plastic will set up wherever it is located, thus a delay caused by such things as pump failures and line blockages may result in the catalyst setting up in the mixing chamber or the wellbore.
In lieu of injecting a mixture of plastic and catalyst into formation, attempts have been made to inject the plastic and the catalyst separately into the formation. This procedure obviates the problem of the plastic setting up prior to its entering into the formation. Another problem arises however, because of the difficulty of achieving a good mixture in the formation. A catalyst may not reach substantial portions of the plastic, resulting in a poor consolidation job. Such poor consolidation will often result in a totally unsatisfactory consolidation.
An additional method of stabilizing an unconsolidated formation comprises coking formation fluids by reverse burn in situ combustion process. In such a process, air used to support the combustion of the formation fluids is flowed countercurrent to the direction of the burn. This is ordinarily accomplished by injecting air through an injection well and providing heat at the production well. Once ignition occurs, the flame front will move toward the source of oxygen, i.e., the injection well. The characteristic of such a reverse burn in situ combustion process is that a residue of coke is left on the particles on the formation. This coke residue effectively bonds together the sand grains making up the formation. If often proves difficult to maintain permeability in the formation when coking is accomplished by reverse burn.
Because of the shortcomings of present sand control methods, it is an object of the present invention to provide improved methods of sand control.